LeetCode Online Judge 题目C# 练习 - Maximum Subarray

Find the contiguous subarray within an array (containing at least one number) which has the largest sum.
For example, given the array [−2,1,−3,4,−1,2,1,−5,4],
the contiguous subarray [4,−1,2,1] has the largest sum = 6.
More practice:
If you have figured out the O(n) solution, try coding another solution using the divide and conquer approach, which is more subtle.

        public static int MaximumSubarray(int[] A)
        {
            int n = A.Length;
            int max = A[0], max_neg = A[0], sum = 0;
            bool flag = false; // for all the elements are negative integers
            for (int i = 0; i < n; i++)
            {
                //if found one is not negative, toggle flag. And keep tracking the max negative number
                if (A[i] >= 0)
                    flag = true;
                else if (A[i] > max_neg)
                    max_neg = A[i];

                sum += A[i];
                if (sum < 0)
                    sum = 0;
                else if (sum > max)
                    max = sum;
            }

            return flag ? max : max_neg;
        }

代码分析：

　　O(n)的解法， 要注意所有element都是negative的case。